This invention relates to particle size measuring instruments and more particularly to instruments which measure the particle size entrained in a fluid stream by means of the light scattered from the particles as they pass through a laser beam.
In U.S. Pat. No. 4,842,486, issued June 27, 1989, invented by Kenneth P. VonBargen, and assigned to the assignee of this application, there is disclosed a particle size measuring instrument of the type to which the present invention pertains. As disclosed in the above-identified application, the particles entrained in a fluid stream are caused to flow through a laser beam in an enclosed channel and light scattered from the particles as they pass through the beam are detected by photodetectors. The height and length of the pulses generated by the photodetectors in response to the particles provide an indication of the size of the particles.
In the above described system, the ability of the instrument to distinguish the pulses caused by particles from noise depends upon the amplitude of the pulses generated. By increasing the intensity of the laser beam, the amount of light scattered from the particles and, thus, the amplitude of the pulses generated by a given particle size can be increased. Accordingly, smaller particles can be detected.